Heretofore, as a method for fluorinating all of C—H portions in a C—H containing compound to C—F, a method of employing cobalt trifluoride, a method for direct fluorination by means of fluorine gas, or a method of carrying out a fluorination reaction by using, as a fluorine source, hydrogen fluoride formed by electrolysis in an electritic cell (electrochemical fluorination, hereinafter referred to as ECF method), has been known. The method of employing cobalt trifluoride is one wherein the reaction is carried out by a gas-solid reaction at a high temperature, whereby there is a problem such that isomerization or bond breakage is likely to take place, to form various types of by-products. While, the fluorination reaction by ECF method has had a problem such that an isomerization reaction takes place, or a problem such that breakage of the main chain or a rebonding reaction is likely to take place, and thus has had a problem that the desired compound can not be obtained with good purity.
In a case where a fluorination reaction is carried out by means of fluorine gas, a method of carrying out the reaction in a gas phase and a method of carrying out the reaction in a liquid phase, are known. However, the gas phase reaction has a problem such that breakage of C—C single bonds takes place during the fluorination reaction to form various types of by-products. In recent years, a method of carrying out the reaction in a liquid phase has been reported. For example, a method of carrying out fluorination in a liquid phase by reacting fluorine gas to a non-fluorinated compound in a liquid phase (U.S. Pat. No. 5,093,432), has been reported. Further, a method for obtaining an acid fluoride compound by pyrolyzing a perfluorinated ester compound, is also known, and it is disclosed that such a compound can be obtained by directly fluorinating a hydrocarbon type ester compound having the corresponding structure by means of fluorine gas in a liquid phase (J. Am. Chem. Soc., 120, 7117 (1998)).
In a case where a fluorination reaction is carried out by means of fluorine gas in a liquid phase, it is common to employ a solvent capable of dissolving fluorine gas, as the solvent of the reaction. However, a hydrocarbon compound as the starting material in the conventional method usually has a low solubility to a solvent which is commonly used for the fluorination reaction. Accordingly, the reaction is carried out at a very low concentration, whereby there has been a problem that the production efficiency is poor, or the reaction will be a reaction in a suspension system which is rather disadvantageous. Further, if it is attempted to directly fluorinate a low molecular weight hydrocarbon compound like one having a molecular weight of less than 200, in a liquid phase, there has been a problem that the yield in the reaction tends to be remarkably low.
On the other hand, as a method for producing a fluorinated ketone, a method is known wherein a partially fluorinated ester is perfluorinated by ECF method, followed by a dissociation reaction to obtain a fluorinated ketone (U.S. Pat. No. 3,900,372). However, the method employing ECF method has the above-mentioned drawbacks and a problem that the yield is low. Especially when an etheric oxygen atom is present in the structure of the compound, there has been a drawback that due to the cleavage of the C—O bond, the yield in the fluorination reaction tends to be extremely low.
Further, a method for obtaining a ketone by dissociating a perfluoroester, is known (U.S. Pat. No. 5,466,877). However, if a fluorination reaction is employed for the step of producing a perfluoroester in the method, there has been a problem that supply of the ester tends to fail, or the reaction system tends to be non-uniform.
It is an object of the present invention to provide an industrial process, whereby a fluorinated ketone can be produced efficiently and at a low cost.